The Liquid Crystal Display (LCD) is a common display device, and possesses properties of low power consumption, small volume and light weight. Therefore, it has been favored by the users. The liquid crystal display generally comprises the backlight module and the liquid crystal panel. The backlight module is employed to provide a plane light source for the liquid crystal panel, and the liquid crystal panel is employed for showing pictures, texts. In the driving circuit of the liquid crystal panel, the P-gamma chip provides the driving voltages of respective gray scales to the liquid crystal panel, and the driving voltage performs polarity reversal. Therefore, the driving voltage is symmetrical relative to the center of the common voltage (VCOM). In other words, the common voltage is at the position where the polarity reversal driving voltage is symmetrical. When the common voltage is at the position where the polarity reversal driving voltage is symmetrical, the flicker generated by the liquid crystal panel is the smallest. In general, the driving voltage and the common voltage of the liquid crystal panel are set at the position of the smallest flicker as the common voltage is at the 128th gray scale. However, due to the unstability and the aging of the thin film transistors in the liquid crystal panel, the outputted common voltage will decay or change inside the liquid crystal panel. The common electrode and the driving voltage which the liquid crystal molecules actually accept will change along with the various positions of the liquid crystal panel and the various lighting period. Therefore, the driving voltage will be no longer symmetrical relative to the common voltage. Meanwhile, with the increase of the lighting period of the liquid crystal panel, the drift phenomenon of the common voltage gets more serious. The degree of asymmetry of the driving voltage relative to the common voltage increases, accordingly. The flicker of the liquid crystal panel is amplified, and thus to influence the display quality of the liquid crystal panel.